Don't panic, there's not been a coup, merely the ending of the business of Parliament in preparation for the General Election in May. The process is an ancient one called "Prorogation" or suspension of Parliament prior to its dissolution on Monday. From then until the State Opening there will be no MPs and those elected in 2010 are banned from entering the Houses of Parliament until after the election. Many will not be contesting the 2015 election but those who are will be merely candidates.
The process of Prorogation is the prerogative of the Queen however this year marks a significant change in the British constitution and one of the Acts which now comes into force changes a constitutional provision that has been in place for 300 years.
Unlike the State Opening of each year's session, the Queen does not personally attend for Prorogation. Instead she appoints a Commission to act on her behalf "under the Great Seal". The final work of the Parliament is for the Commons to attend the Lords after being summoned by Black Rod. As at the opening, the door to the chamber is slammed in his face. As a representative of the Queen he must ask permission to enter.
Once in the Lords, the names of the bills passed by the Commons and Lords as yet not Acts are read. After each, the Clerk of Parliament uses the Norman French phrase "La Reigne le veult" or "The Queen Agrees" or more literally, "the Queen raises it" [from a bill to an Act]. If there is not other implementation date or if it is not subject to a later order, the now Act's provisions come into effect at midnight.
This year one of those new Acts change the succession to the throne in two ways. First, "Primogeniture" is abolished. That was the right of the first born son to succeed after the death of the previous monarch. Now it is simply the first born. While this will not affect the line from Elizabeth to Charles to William to George; it may affect the position of the new child William and Kate are expecting. If it is a girl; she will now follow George in the line of succession whether or not any future child is a boy.
Since 1701, the Act of Settlement has banned a British monarch from marrying a Roman Catholic. One of the Acts passed today removes that prohibition but the monarch, as titular head of the Church of England must still be protestant. Incidentally, the Act of Settlement also provided for:
No foreigner, even if naturalised (unless born of English parents) shall be allowed to be a Privy Councillor or a member of either House of Parliament, or hold "any office or place of trust, either civil or military, or to have any grant of lands, tenements or hereditaments from the Crown, to himself or to any other or others in trust for him."
Although subsequent British nationality laws made naturalised citizens the equal of those native born so this provision no longer applies; it is echoed in the US Constitution's requirement that the President be a "natural born citizen".
After the formal Royal Assent has been given, the head of the Commission reads a "Queen's Speech" on her behalf summing up the work of the Parliament. In practice this is written by the outgoing government. The Commons then return to their chamber for the final formal business, the confirmation of the bills receiving Royal Assent and the instrument of Prorogation.
Another constitutional change comes into effect this year. Instead of the dissolution being a simple Royal Prerogative, although requested by the Prime Minister; the Fixed Term Parliament Act 2011 now provides for a 5 year term. There are provisions to call an early election which I'll comment on later but otherwise the timetable is fixed.
After Prorogation, MPs have a few days to "clear their desks" but at midnight on Sunday they cease to be Members. The General Election campaign formally starts.
Now one thing you will no doubt be wondering is the prospects for the result. Almost certainly there will be no single party with an outright majority. The most likely outcome is a minority Labour or Conservative government supported by another party in a "supply and confidence" agreement, not a new coalition. Under that, the minor party would agree to support government budgets and vote against votes of no confidence. Here is where the Fixed Term Parliament Act has an effect.
Previously, a government would fall if the Commons passed a vote expressing no confidence in it and the Prime Minister would ask the monarch to call a new election. Now an early election can only be called after a further vote of no confidence or by 2/3rds of the House passing a motion to call one (the number includes vacant seats).
That provision is so that either the government can reach another agreement or another party can form a new government and a vote of confidence in that new government is passed within 14 days. If no such new arrangement has been reached and the Commons again passes a motion of no confidence by a simple majority, a General Election is called and the fixed 5 year term runs from the date of it.
The interesting part of a minority or coalition government is that it inevitably involves the monarch in some of the background negotiations. In 2010 Gordon Brown hung on while an attempt was made to form a Labour/Liberal Democrat coalition (although it has to be said the negotiations by the Labour team were half hearted at best). There was pressure to form a government before the Monday after the election because of the money markets opening. You may recall at that time there was a bit of financial problems for the UK (an outgoing Treasury minister wrote to his successor "There's no money left") Behind the scenes, a palace official was facilitating the negotiations between the parties as an "honest broker". This year it will likely take rather longer than two or three days to come to a new settlement. If Cameron, even if leading the largest party, cannot form a new government before the opening of Parliament in late May, he will face a vote of no confidence. Before then, it is likely that he would advise the Queen of the situation and she would ask Labour to attempt to form one.
By convention, the Prime Minister has to resign before the Queen can ask somebody else to form a government. Usually this is where the PM decides to step down in favor of a replacement leader of their party. The process is therefore quite simple if a single party has a majority. The outgoing PM recommends that the new party leader be asked and things are fairly automatic.
Supply and confidence agreements leads to quite unstable government. It certainly restricts the amount of radical legislation that can be passed easily. A new election would be likely before the end of the 5 year term.